1. Field of the Invention
The present invention relates to a fuel cell control device and to a fuel cell vehicle control apparatus, and in particular relates to a technology for controlling operations of the fuel cell when a supply flow rate and a supply pressure of a reaction gases supplied to the fuel cell changes with atmospheric pressure change.
2. Description of the Related Art
Conventionally, a fuel cell stack (hereinafter, called a fuel cell) is constituted by a plurality of cells, each of which is formed by providing a pair of electrodes on opposite sides of a solid polymer electrolyte membrane. In this fuel cell, hydrogen as a fuel gas is supplied to an anode, and air as an oxidant gas is supplied to a cathode and hydrogen ions generated by the catalyst reaction at the anode move to the other electrode via the solid polymer electrolyte membrane. The hydrogen ions, after being transferred to the cathode cause a electrochemical reaction with oxygen at the cathode for generating electric energy.
The fuel cell as described above comprises an air compressor, for example, for supplying air to the cathode of the fuel cell, and a pressure flow rate control valve for supplying hydrogen to the anode of the fuel cell by use of the pressure of air as a signal pressure. That is, the fuel cell is designed so as to ensure a predetermined generation efficiency by setting the anode side reaction gas pressure at a predetermined pressure depending upon the cathode side pressure.
However, in a fuel cell according to one example of the conventional fuel cells, it is not possible to supply the reaction gases at a desired pressure and desired temperature, when the vehicle travels to locations at high altitude.
That is, as the altitude increases, the atmospheric pressure decreases and air becomes rarefied. Therefore, in order to acquire a desired amount of electric energy, it is necessary to increase the flow rate (mass flow rate) of the reaction gas and to maintain the pressure of the reaction gas at a predetermined pressure by increasing the rotation speed of the compressor. However, if it is required to increase the rotation of the compressor to an extent exceeding the capability of the air compressor, it becomes difficult to supply the reaction gas at a desired flow rate level and a desired pressure level.
In the state in which the reaction gas at a desired pressure and a desired flow rate is not supplied to the fuel cell, when the fuel cell is required to generate a predetermined electric current based on a predetermined generation command, a problem arises in the generation voltage of the fuel cell becomes unstable or the generation voltage falls too low far a predetermined voltage. Furthermore, since the generated current is output from the fuel cell while the reaction gas is insufficiently supplied, there is a possibility that the solid polymer membrane of the fuel cell will be deteriorated or that the long-term durability of the fuel cell will be degraded